Hello everyone! I too had this problem and fixed it.
When you are on the airplay selection area on the Apple TV (hold down the tv icon on remote & a small menu opens up, scroll down to the airplay icon), change between tv speakers and the HomePod and eventually it starts to play. For me I first had the pod selected and no sound coming then I also selected tv speakers and it automatically switched to the pod and started playing. Might not work for everyone, but okay around with it and it might just work for you!